The present invention relates to a spliceable elastic laminate having rubber properties and comprising two mutually joined layers that consist of non-polar hydrocarbon compounds, of which one layer is a thermoplastic elastomer (TPE) and the other is a cross-linked vulcanized rubber of the EPDM type or the butyl type. The laminate is primarily intended for use as a sealing sheet or membrane in different types of building construction work, although it may also find use in other areas in which the possibility to splice or join rubber is highly desirable. Rubber suits, such as diving suits and protective suits are examples of this latter field of use.
By xe2x80x9crubber propertiesxe2x80x9d is meant in the present context the unique properties associated with the fact that rubber is a cross-linked material which is able to take-up significant movements under the most varying climatic conditions without rupturing or being permanently deformed when subjected to moderate loads.
Hitherto, it has only been possible to join together two sheets of rubber with an homogenous splice that has rubber properties by vulcanizing said sheets together. Vulcanization of the sheets is effected by placing a splicing strip of non-vulcanized rubber between mutually overlapping rubber sheets and then applying pressure and heat to the splice over a given period of time. The length of time required to complete the process has greatly limited the use of rubber-based sheets in those applications where splicing is necessary, for economic reasons.
Other splicing methods have also been tried, such as gluing or like methods. These methods, however, also have serious limitations with respect to productivity and durability. They are also detrimental from an environmental aspect, because of the need to use undesirable solvents.
In the case of building or construction applications, such as the use of waterproof membranes as roof coverings or in the construction of tunnels, bridges, dams, swimming pools, and other similar applications, the difficulties experienced in splicing together rubber sheets has often resulted in the preference to use non-elastic sealing products or waterproofing membranes that are based on bitumen or thermoplastic materials which can readily be spliced by fusing together material surfaces in a splice overlap, e.g. by heating said surfaces with hot air or in some other appropriate manner and then applying pressure to said surfaces as the materials cool.
Several methods of avoiding the aforedescribed problems associated with the use of rubber where splicing is required have been suggested.
JP-A-60 203640 teaches a method of avoiding problems when splicing rubber in the production of a waterproof sheet, simply by positioning a layer of rubber and a thermoplastic elastomer with the surfaces to be joined together overlapping one another and thereafter heating the sheets to a temperature of 400-600xc2x0 C. by means of a hot-air gun. The thus heated sheets are then pressed together with the aid of a pressure roller at 5-10 kg/cm to form said splice or join. It will be understood that the application of this method is limited by the high material costs and working costs involved.
EP-A1-0 528 296 describes a rubber splice or join and a method of splicing an intermediate sheet of thermoplastic polyolefin film between the overlapping surfaces of rubber sheets. The join, or splice, is effected by heating the overlapping surfaces to a temperature slightly above the melting point of the thermoplastic film. This method is said to produce a join with higher productivity and greater strength than a glued join between rubber sheets. However, the elastic properties of the join are reduced in comparison with the join obtained by vulcanization with an intermediate rubber sheet as described above. This also presents a complication in comparison with the use of fusible thermoplastic sealing material, as before mentioned.
U.S. Pat. No. 3,962,018 teaches a method of producing multi-layer composites from plastic and rubber, wherewith one layer comprises a mixture of thermoplastic polyolefin and 10-40% by weight elastomer fused together at a temperature higher than 150xc2x0 C. The mixture is applied to an elastomeric surface (EPDM or butyl rubber) that has been heated to 150xc2x0 C., whereafter the layers are joined together by heating said layers to about 150-250xc2x0 C. and pressing said layers with a pressure of between 1 and 10 kg/cm2. This method enables the covering materials to be placed and joined together to form a multi-layer composition in a continuous process. The covering material, however, consists mainly of a thermoplastic material, which does not have the elastic properties required for coacting with the rubber and therewith provide a finished product that has rubber properties.
EP-A1-0 693 367 teaches a laminate that is produced by joining a polymer film to vulcanized EPDM rubber, or by extruding said film and rubber together and then vulcanizing the product obtained. In this particular case the polymer film is based on polyamide and/or polyethylene, copolymers of ethylene, polypropylene, or copolymers of propylene. Since manufacture, including shaping of said layers, placing said layers together and joining together said layers, is effected in a continuous process, the laminate product is attractive from the aspect of cost but is still insufficiently elastic to be measured against rubber with respect to splicing or joining the product.
The inventive laminate is intended to provide a material that has rubber properties and that is not encumbered with the aforesaid problems regarding spliceability that are otherwise associated with rubber material or with insufficiently elastic joins and splices that are associated with hitherto known rubber/polymer laminates. The laminate can thus be used advantageously as a sealing membrane for roof coverings and similar building applications where simple and quick splicing/joining is a pronounced desideratum.
Accordingly, there is provided in accordance with the invention a spliceable elastic laminate that has the features set forth in the accompanying product claim, and a method of producing such a laminate in accordance with the method steps set forth in the method claims.
As mentioned in the introduction, the inventive laminate is comprised of two mutually joined layers built-up of non-polar hydrocarbon compounds, of which one sheet or layer is comprised of a thermoplastic elastomer (TPE) and the other is comprised of cross-linked vulcanized EPDM rubber or butyl rubber. The laminate is characterized in that the thermoplastic elastomer includes at least 10% by weight of an elastic copolymer that can be mixed with filler and fire retarding agent to a mixture containing at least 50% by weight filler.
A thermoplastic elastomer (TPE) is an elastomer, i.e. a polymeric material, of high elastic stretchability in which the cohesive forces necessary for the elastic deformation of the material are of a physical nature and which can be nullified by heating or melting the material, as distinct from rubber, whereby the material becomes plastically formable at elevated temperatures and returns to its highly elastic state when cooled.
The elastic copolymer used will conveniently be one that contains ethylene and octene in the ratios of from 1:10 to 4:10, preferably ratios from 2:10 to 3:10. The copolymer may also conveniently contain petroleum resin in an amount corresponding to 1-20% by weight, which provides good adhesiveness and adapts viscosity and elasticity.
The thermoplastic elastomer will also suitably contain a filler in an amount corresponding to 20-80% by weight, preferably 40-60% by weight. The filler may suitably be calcium carbonate, carbon black or silicate. The aforesaid flame resistant agent may be aluminium hydrate or magnesium hydrate.
The composition of the thermoplastic elastomer may conveniently be such as to impart to the elastomer a viscosity of within 0.01-1 Nm, preferably 0.05-0.6 Nm within a temperature range of 70-150xc2x0 C. The viscosity of this layer can herewith be optimized to obtain good adhesion (wetting) to the EPDM-layer when heat welding said layers together, and to avoid the laminates sticking together when vulcanizing or handling said laminates and when storing said laminates in roll form.
Both of the layers in the laminate may conveniently include peroxides in an amount corresponding to less than 1% by weight, with the intention of improving cross-linking through the medium of carbon-to-carbon bonds with the thermoplastic elastic layer.
The thermoelastic layer in the laminate will normally have a thickness smaller than 0.5 mm, while the thickness of the rubber layer will be greater than 0.5 mm. A suitable thickness range with respect to the thermoelastic layer is 0.2-0.4 mm, and from 0.7-0.9 mm with respect to the rubber layer. If considered appropriate, a filament reinforcement may be included in the rubber layer and/or in the thermoelastic layer. The thermoelastic layer may incorporate predetermined colors for given purposes significant to the design of roofs and roof systems and also to improve thermal reflection.
When covering a roof or when using the laminate in similar applications, the thermoelastic layer will face towards the underlying supportive surface and overlap the adjacent part of the laminate that faces away from said surface, i.e. the rubber layer, in the join locations.
The inventive laminate is produced by calendering or extruding non-vulcanized EPDM rubber or butyl rubber and thermoplastic elastomeric (TPE) foil or film containing at least 10% by weight elastic copolymer to form a continuous foil web. The web is then rolled-up on a drum and thereafter vulcanized, for example in an autoclave. Although the thermoplastic elastic and the rubber will stick together in this case and the rubber be cross-linked and therewith unmeltable in the present terms, the thermoplastic elastic layer will retain its thermoplastic properties and form a meltable layer. By xe2x80x9ccalenderingxe2x80x9d is meant processing in a machine that includes two or more rolls equipped with devices for heating and cooling at adjustable distances therebetween. By xe2x80x9cextrusionxe2x80x9d is meant here so-called broad-slot extrusion in which the input components are extruded through a flat nozzle that has a broad orifice, i.e. an orifice of small height in relation to width.
A suitable type of rubber for use with the invention is an ethylene propylene rubber (EPDM) based on terpolymers of ethylene, propylene and a diene, whose remaining unsaturated part enters into the side position of the main chain.